At least a dozen relatives of people murdered by teenagers gathered Wednesday at the State House, where they urged legislators to support a bill that would keep juveniles convicted of first-degree murder behind bars for at least 35 years before having a chance at parole.

Jen Boisvert, a cousin of Amy Carnevale, a 14-year-old Beverly cheerleader who was beaten and stabbed to death by her 16-year-old boyfriend in 1991, said the family is distraught over a recent court ruling that grants Carnevale’s killer, and other such offenders, a chance of being freed on parole.

“We had a small amount of peace knowing that the perpetrator was in his cell and that the community was safe,” Boisvert said. “We are faced with the terrifying possibility that Amy’s killer could live among us again . . . Didn’t our family suffer enough when sweet Amy was brutally murdered?”

It is unclear how the bill, introduced by Republican Senator Bruce Tarr, will fare.

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Governor Deval Patrick said he supports separate legislation that would grant parole eligibility after about 20 years.

“I’m very sympathetic to the families,” Patrick said.

Tarr introduced his bill after a Supreme Judicial Court ruling in December 2013 declared it unconstitutional to deny parole to inmates sentenced to life in prison for a murder they committed while a juvenile, defined as age 17 or younger. The decision means that 65 inmates sentenced for first-degree murder as juveniles will for the first time have a chance at freedom.

For years, first-degree murder convictions led to automatic sentences of life in prison without parole. But a 2012 US Supreme Court decision found it was unconstitutional to sentence a teenager to life in prison without the possibility of parole. That led the state’s top court to issue a similar ruling in December.

William Brownsberger, Senate chairman of the Legislature’s Joint Committee on the Judiciary, said Wednesday that he is concerned about passing legislation that does not differentiate between young killers who carefully planned the brutal executions of their victims and juveniles who acted recklessly because of peer pressure. He said the committee will review at least a half-dozen bills filed following the court rulings — each bill has different recommendations for how long an inmate would need to serve before being eligible for parole. Tarr’s bill asks for the longest amount of prison time.

Opponents of that bill, among them retired judges and the mother of a murder victim, also testified before the committee, urging legislators to believe in the possibility of rehabilitation.

“We can’t ignore that” science, retired Juvenile Court judge Martha Grace told the committee. “Those issues that we may have intuited as judges are now borne out by research. Many actions are done in the spur of the moment or because of peer pressure. Not that these are excuses for their behavior, but they have to be looked at.”

Clementina Chery, a well-known antiviolence activist whose 15-year-old son was murdered in gang cross-fire in 1993, said she supports parole eligibility after 15 years. The man convicted of killing her son was in his 20s and pleaded guilty to second-degree murder. Chery said she has worked closely with the shooter’s family and supported his bid for parole after 15 years.

“I believe if I had opposed his parole he would have never seen the light of day,” she said. “A child who committed the crime may still have a chance, a hope that life can be meaningful . . . There is hope that there can be some redemption, healing, and reconciliation and the possibility of doing some good in this world.”

But for families of other victims, that possibility seemed remote.

“Every time I hear that juvenile brains are not as developed, I want to scream at the top of my lungs out of frustration,” said Ryan Downing, whose mother, Janet, was murdered in 1995 by his best friend at the time, Edward O’Brien.

O’Brien was 15 when he stabbed Downing almost 100 times in her Somerville home.

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